The aim of the study is to determine whether switching from an antiretroviral regimen containing abacavir and/or didanosine to one containing maraviroc will lead to a reduction in platelet reactivity and inflammatory markers at weeks 12 and 24 thereby conferring a reduction in cardiac risk.

In addition the study will assess the efficacy of a maraviroc containing regimen in combination with a boosted protease inhibitor in terms of tolerability and achieving long term viral suppression as assessed at week 48.

The investigators hypothesize that there will be a rapid reduction in platelet reactivity on switching to maraviroc and that a boosted protease inhibitor in combination with maraviroc will provide a safe and efficacious antiretroviral regimen enabling a reduction in cardiac risk whilst maintaining virological suppression.

To assess for the following: Mean change over 24 weeks and mean difference at week 12 between study groups in plasma inflammatory and cardiac biomarkers and markers of immune activation [ Time Frame: 48 weeks ]

any licensed boosted protease inhibitor at any dose (excluding tipranavir*)

Undetectable plasma HIV RNA to less than 50 copies/mL for at least 24 weeks prior to screening

Availability of stored plasma with which to perform a tropism assay

CCR5 tropic HIV virus based on a tropism assay from a stored plasma sample

Willing to continue unchanged, or to modify antiretroviral therapy, in accordance with the randomisation assignment

No documented viral resistance to currently licensed HIV-1 protease inhibitors based either on previous HIV-1 genotypic resistance testing or in the judgement of the study investigators

No previous exposure to maraviroc or CCR5 receptor antagonists

Subjects in good health upon medical history, physical exam, and laboratory testing in the opinion of the investigator

Female subjects who are heterosexually active and of childbearing potential (i.e., not surgically sterile or at least two years post menopausal) must avoid becoming pregnancy as follows from screening through completion of the study using one or both of the following methods:

barrier contraceptives (condom, diaphragm with spermicide)

IUD PLUS a barrier contraceptive

Female subjects of childbearing potential must have a negative pregnancy test

Exclusion Criteria:

failure of current antiretroviral regimen due to virological failure

active opportunistic infection, malignancy or significant co-morbidities in the opinion of the investigator

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Please refer to this study by its ClinicalTrials.gov identifier: NCT00981773